The present invention relates to a control valve for a variable capacity compressor used in an air conditioning device for vehicles and the like, and more specifically relates to a control valve for a variable capacity compressor that controls according to need the supply of refrigerant gas from a discharge pressure region to an intermediate pressure region of the compressor.
Heretofore, a variable capacity compressor equipped with a cylinder, a piston, a cam plate and the like is used for example to compress and discharge a refrigerant gas in an air conditioning device mounted on a vehicle. A known control valve for the variable capacity compressor comprises a refrigerant gas passage that communicates a discharge pressure region with a crank chamber that is in an intermediate pressure region, and by adjusting the pressure within the crank chamber, the tilt angle of the cam plate is changed so as to vary the discharge capacity. The pressure adjustment within the crank chamber is performed by adjusting the opening of the control valve mounted between the refrigerant passage, thereby supplying a high-pressure compressed refrigerant gas from the discharge pressure region to the crank chamber.
One typical type of control valve mentioned above is shown in FIG. 3 as a control valve 100 for a variable capacity compressor (hereinafter called xe2x80x9ccontrol valvexe2x80x9d) (refer to Japanese Patent Laid-Open Publication No. 2000-120912). The control valve 100 is mounted to the rear housing side of the variable capacity compressor, and mounted via o-rings 121a, 121b, and 131b so as to maintain an airtight state, thereby adjusting the pressure within the crank chamber of a variable capacity compressor.
The control valve 100 comprises a control valve body 120, a solenoid excitation unit 130, and a pressure sensitive unit 145, wherein the solenoid excitation unit 130 is positioned at the center of the control valve 100 and to both sides of the solenoid excitation unit 130 are positioned the control valve body 120 and the pressure sensitive unit 145.
The solenoid excitation unit 130 comprises on the outer circumference thereof a solenoid housing 131, and in the interior of the solenoid housing 131 are positioned a solenoid 131A, a plunger 133 that moves up and down by the excitation of the solenoid 131A, and a magnetic drawer 141. A plunger chamber 130a housing the plunger 133 is communicated to a suction refrigerant port 129 equipped to the control valve body 120. Further, the solenoid 131A is connected with a cord (not shown) that is capable of supplying excitation current controlled by a control computer (not shown).
The pressure sensitive unit 145 is positioned below the solenoid housing 131, and in the inside thereof is formed a pressure sensitive chamber 145a. The pressure sensitive chamber 145a includes a bellows 146 and a pressure sensitive spring 159 that operates the plunger 133 through a stem 138 and the like, and the interior of the pressure sensitive chamber 145a is maintained at a vacuum state.
The control valve body 120 comprises a valve chamber 123, and a valve means 132 that opens and closes by the plunger 133 is positioned within the valve chamber 123. A refrigerant gas having a high discharge pressure Pd is introduced to the valve chamber 123 through the discharge pressure region of the compressor and the discharge refrigerant port 126. On the bottom surface of the valve chamber 123 is formed a valve hole 125 that communicates to a crank chamber refrigerant port 128, and the upper space within the valve chamber 123 is sealed by a stopper 124. At the center of the stopper 124 is created a pressure chamber 151 formed as a vertical hole with a bottom having a cross-sectional area equal to the valve hole 125 and opposing to the valve hole 125. The pressure chamber 151 is also formed as a screw storage chamber 151a, to the bottom of which is positioned a valve closing spring 127 that biases the valve means 132 toward the bottom surface of the valve chamber 123.
The valve means 132 is a shaft-like body including an upper portion 132a, an enlarged valve portion 132b, a small-diameter portion 132c and a lower portion 132d. The upper portion 132a and the lower portion 132d have the same cross-sectional area as the valve hole 125. The upper portion 132a is fit to and supported by the stopper 124 having the pressure chamber 151, the enlarged valve portion 132b is positioned inside the valve chamber 123, and the small-diameter portion 132c opposes a crank chamber refrigerant port 128 that communicates to a crank chamber (intermediate pressure Pc)within the valve hole 125. The lower portion 132d is fit to and supported by the control valve body 120, the end portion of which is inserted to a plunger chamber 130a into which a refrigerant gas having a suction pressure Ps is introduced, being contacted to the plunger 133. The valve means 132 moves up and down along with the vertical movement of the plunger 133, and the enlarged valve portion 132b of the valve means 132 adjusts the gap between a valve seat 125a on the upper surface of the valve hole 125. The low-temperature suction pressure Ps introduced to the plunger chamber 130a enters the pressure sensitive portion 145.
The stopper 124 is equipped with a horizontal hole 153 that communicates to the pressure chamber 151, and the horizontal hole 153 communicates the pressure chamber 151 with a gap portion 139 defined by the stopper 124 and the control valve body 120. On the other hand, the control valve body 120 is equipped with a cancel hole 155 that communicates the gap portion 139 with the plunger chamber 130a into which the refrigerant gas having a suction pressure Ps enters. Accordingly, the refrigerant gas having a suction pressure Ps inside the plunger chamber 130a is introduced to the pressure chamber 151 through the cancel hole 155, and the valve means 132 receives the suction pressure Ps from both the upper and lower portions 132a and 132d. Moreover, since the upper and lower portions 132a and 132d of the valve means 132 have the same cross-sectional areas, the suction pressure Ps received from the upper and lower portions 132a and 132d are balanced and cancelled, so that the valve means 132 will not substantially be influenced by the discharge pressure Pd. Moreover, the valve means 132 includes a small-diameter portion 132c positioned near the crank chamber refrigerant port 128 having a crank chamber pressure Pc, so when the valve portion 132b of the valve means 132 is seated on the valve seat 125a, the valve means 132 will not receive unnecessary pressure even when the pressure Pc within the crank chamber is loaded, since the forces toward the upper and lower directions are balanced.
A plunger 133, to which is fixed the valve means 132, is mounted inside the solenoid housing 131, and the plunger 133 is slidably supported by a pipe 136 that contacts the end portion of the control valve body 120 tightly through an o-ring 134a. The upper end 138A of a stem 138 is inserted and fixed to a storage hole 137 formed to the lower end of the plunger 133, and the lower end 138B of the stem 138 is supported slidably against the magnetic drawer so that it protrudes from the upper storage hole 142 of the drawer 141 toward the lower storage hole 143. A valve opening spring 144 is positioned between the plunger 133 and the upper storage hole 142 of the magnetic drawer 141, biasing the plunger 133 toward the direction separating from the magnetic drawer 141.
Further, out of the pair of stoppers 147 and 148 inside the bellows 146 positioned within the pressure sensitive chamber 145a, the stopper 147 is mounted to the lower portion 138B of the stem 138, the stopper 147 being able to move away from the stem. A spring 150 biasing the stopper 147 away from the magnetic drawer 141 is positioned between the flange 149 of the stopper 147 and the lower storage hole 143 of the magnetic drawer 141.
When the suction pressure Ps inside the pressure sensitive chamber 145a rises, causing the bellows 146 to shrink, the pair of stoppers 147 and 148 come into contact with each other and regulates the disposition of the bellows 146. The maximum disposition of the bellows is set so as to be smaller than the maximum fitting quantity of the lower portion 138B of the stem 138 with the stopper 147 of the bellows 146.
When the operation switch of the air conditioning device is turned on, and if for example the detected temperature is equal to or above a predetermined temperature, the computer orders excitation of the solenoid 131A of the control valve 100. Thereby, the plunger 133 is pulled toward the magnetic drawer 141, the valve means 132 contacting the plunger 133 moves toward the direction to close the valve hole 125, and the flow toward the crank chamber is stopped. On the other hand, the low-temperature refrigerant gas is introduced from said suction pressure region into the pressure sensitive portion 145 through the suction refrigerant port 129 and the plunger chamber 130a of the control valve body 120. The bellows 146 at the pressure sensitive portion 145 is displaced based on the pressure of the refrigerant gas at a suction pressure Ps, and the displacement is transmitted via the stem 138 and the plunger 133 to the valve means 132. In other words, the opening position of the valve means 132 against the valve hole 125 is determined by the suction force of the solenoid 131A, the bias force of the bellows 146, and the bias force of the valve closing spring 127 and the valve opening spring 144.
When the pressure (suction pressure Ps) within the pressure sensitive chamber 145a rises, the bellows 146 contracts, and since the contraction direction corresponds to the direction in which the solenoid 131A pulls the plunger 133, the displacement of the bellows 146 is followed by the movement of the valve means 132, and the opening of the valve hole 125 reduces. Thereby, the amount of high-pressure refrigerant gas introduced from the discharge pressure region into the valve chamber 123 is reduced (the crank chamber pressure Pc drops), and the tilt angle of the cam plate is increased. Moreover, when the pressure within the pressure sensitive chamber 145a falls, the bellows 146 expands by the restoration force of the pressure sensitive portion spring 159 and the bellows 146 itself, the valve means 132 moves in the direction to increase the opening of the valve hole 125, increasing the amount of high-pressure refrigerant gas to be introduced to the valve chamber 123 (increasing the crank chamber pressure Pc), and the tilt angle of the cam plate is reduced.
On the other hand, when the heat load becomes smaller, the high-pressure refrigerant gas flows from the discharge pressure region into the crank chamber at the intermediate pressure region, the pressure within the crank chamber rises, and the tilt angle of the cam plate becomes smaller.
In case the pressure difference between the discharge pressure region and the crank chamber becomes smaller than the predetermined value, the flow of refrigerant from the compressor to the condenser is blocked. As explained, when the heat load becomes smaller and the solenoid 131A is demagnetized, the suction against the plunger 133 is stopped, and by the bias force of the valve opening spring 144, the plunger 133 moves toward the direction separating from the magnetic drawer 141, the valve means 132 moves toward the direction releasing the valve hole 125 of the control valve body 120, and the flow toward the crank chamber is accelerated.
When the pressure within the pressure sensitive chamber 145 rises, the bellows 146 contracts, and the opening of the valve means 132 reduces. However, since the lower portion 138B of the stem 138 is removably fit to the stopper 147 of the bellows 146, the displacement of the bellows 146 will not influence the valve means 132.
With regard to the above-mentioned prior-art control valve 100, it is required to reduce the size of the control valve in order to create a small-sized variable capacity compressor to be used in the air conditioning device of a vehicle.
One way to reduce the size of the control valve 100 is to reduce the number of turns (winding number) of the coil of the solenoid 131A. When considering that the solenoid 131A works as the reaction force at the pressure sensitive side, the reduction of the winding number of the coil in the solenoid 131A leading to the miniaturization of the control valve can be achieved by reducing the size of the pressure sensitive chamber 145a, in other words, by reducing the diameter of the bellows 146, and by reducing the size of the pressure sensitive portion spring 159.
However, there is a limit in reducing the space for positioning the pressure sensitive portion spring 159 in the pressure sensitive chamber 145a. For example, if the refrigerant gas being introduced to the compressor has a high pressure of approximately 10 times the normal value, it is difficult to reduce the size of the spring 159 in the pressure sensitive portion. Therefore, there is a need to provide some kind of solution in order to reduce the winding number of the coil of the solenoid 131A that leads to reducing the size of the control valve without mainly changing the spring 159, but the conventional control valve 100 lacks such solution.
The present invention takes the above problems into consideration, and the object of the invention is to provide a control valve for a variable capacity compressor capable of reducing the size of a control valve comprising a spring in the pressure sensitive portion and a bellows.
In order to achieve the above objects, the control valve for a variable capacity compressor according to the present invention comprises a solenoid excitation unit positioned at the center thereof, a control valve body positioned above said solenoid excitation unit, and a pressure sensitive unit positioned below said solenoid excitation unit: wherein the control valve body is equipped with a valve means for opening and closing the passage between a discharge pressure region and an intermediate pressure region of the compressor; the solenoid excitation unit is equipped with a plunger that moves according to excitation, a magnetic drawer, and a bellows for operating the valve means; and the pressure sensitive unit comprises a pressure sensitive unit spring for operating the valve means.
The control valve for a variable capacity compressor mentioned above according to the present invention comprises a bellows that is arranged within the solenoid excitation unit and is separated from the pressure sensitive unit spring in the pressure sensitive unit. This feature of the invention enables the diameter of the bellows to be reduced without having to change the design of the pressure sensitive unit spring, and by reducing the diameter of the bellows the winding number of the solenoid is necessarily reduced, which leads to reducing the overall size of the control valve for a variable capacity compressor.
Moreover, in a preferable embodiment of the control valve for a variable capacity compressor according to the present invention, the pressure sensitive unit is equipped with an atmospheric pressure introducing hole.
Furthermore, in another preferable embodiment of the control valve for a variable capacity compressor according to the present invention, the bellows is arranged along the same axis as the pressure sensing unit spring, or the bellows has a length so as to be extended to both the plunger and the magnetic drawer, or the solenoid excitation unit is equipped with a centralization mechanism positioned at the control valve body side of the bellows.
Even further, the solenoid excitation unit communicates with the suction pressure region of the compressor at the upper end of the control valve body.